This invention relates to an organopolysiloxane composition for viscous fluid coupling. More specifically, this invention relates to a viscous fluid coupling organopolysiloxane composition which is stable for long periods of time and so does not suffer from torque variations at high temperatures and high shear forces.
Because the fluid used for viscous fluid coupling must have properties such as an appropriate viscosity, high flash point, stability against oxidation, stability against thermal decomposition and an insignificant temperature dependence on the part of the viscosity, fluid dimethylpolysiloxanes have generally been used heretofore in this application.
However, by themselves, dimethylpolysiloxane fluids tend to deteriorate after a certain period of time, i.e., suffer from an increase in viscosity or gelation, due to the violent shear forces and frictional heat generated in fluid coupling. Accordingly, they lose their fluid coupling function.
Thus, Japanese Patent 55-18457[18457/80] proposes a working fluid comprising a fluid organopolysiloxane which contains a polysiloxane possessing the N-phenylaminophenyl group and with a degree of polymerization of .ltoreq.40. This working fluid is relatively stable with regard to gelation and viscosity increases at high temperatures and high shear forces.
However, the preceding method suffers from the problem that long-term use in fluid coupling causes a decline in the organopolysiloxane's viscosity due to the high shear forces. A gradual decline in the torque transmission ratio occurs and the fluid coupling function is lost.